Project summary/abstract Severe sepsis is a clinical syndrome occurring in patients with severe injury or infection, with an annual incidence of approximately 750,000 cases in the United States. The mortality rate is 20-30%, and currently there are no specific therapeutic agents approved for clinical use. Indeed, the only specifically approved agent (Xigris) was recently withdrawn from the clinic because of poor efficacy. Autopsy studies have shown that the major cell death mechanism in severe sepsis victims is via programmed cell death through two major pathways, termed apoptosis and pyroptosis. Prior efforts to prevent cell death by blocking the inflammasome had been extremely difficult, because until recently, the identity of a major regulatory protein that controls the inflammasome was unknown. However, an innovative discovery has now revealed the identity of the key regulatory protein that is required for activation of the inflammasome: it is a kinase termed PKR. We have reported this discovery in Nature, and it now enables us to directly target the inflammasome by inhibiting PKR; this also prevents programmed cell death. The objective of this proposal is to study the role of these PKR pathways in the pathogenesis of sepsis. We will use an innovative new approach to focus on the overall hypothesis that pyroptosis during severe sepsis is deleterious, and that inhibiting pyroptosis by inactivating PKR-dependent inflammasome activation will be beneficial to the host. This will be accomplished in three Aims: Specific Aim 1. Role of PKR as an essential regulator of pyroptosis; Specific Aim 2. Role of PKR in inflammasome assembly; and Specific Aim 3. PKR as a therapeutic target in sepsis. The results of this innovative approach should reveal the mechanisms of cell death in severe sepsis, and open a pathway to preventing it with agents that inhibit PKR.